The present invention relates generally to a conveyor system for moving webs or sheets of material with maximum efficiency, with minimum power requirements and with minimal chatter, vibration and deflection. This system is especially suitable for photographic development equipment.
Machines which require an extended transport roller system for carrying a flexible workpiece, like film or papers, are known. Typical prior art types of conveyors are disclosed in U.S. Pat. Nos. 3,336,025 to L yne, 3,078,024 to Sardeson, 3,435,749 to Cauwe et al., and 3,520,461 to Savela.
In typical prior art systems, one cluster of gears is serially connected to the next cluster of gears. As a result the input torque required to overcome friction increases with each added mesh so that the total input torque required is a function of the total number of meshes, bearings, pitch diameters, etc. This is illustrated by the Layne patent.
Moreover, the conveyors of the prior art, such as those Savela and Cauwe et al., have serious operating difficulties in that the long gear train with multitudinous meshing gears from top to bottom has excessive friction and tends to bind. Such gear trains thus limit the height of the unit and the length of the path available for the web. Moreover, such gear trains do not provide uniformity of movement of the web and are subject to vibration and chatter causing unsatisfactory film quality.
The gear drives of the prior art conveyors follow accepted principles of design that a continuous train is simplest to design, assemble and service, that a continuous gear train of the smallest possible gears produces a lighter weight and smaller overall package, that the use of small diameter gears minimizes gear cost and results in an optimum gear quality, and that the smaller diameter gears have a lower pitchline velocity and will therefore wear less, last longer and be quieter in action and will give less of a thermal expansion problem.
Thus, the web transport systems of the prior art, with their long series of driven roller assemblies, are beset with the problem of the transmission of power to all these rollers through the corresponding long train of meshing power transmitting gears. For such gear trains, input torque required to overcome friction increases with each added meshing. The difference between the magnitudes of output and input power is attributable to losses due to gear teeth meshing and shaft bearing friction. Such conventional systems show a relatively rapid fall-off of efficiency with length. As shown by conventional systems in use, the number of rollers which can in practice be driven by such a system is severely limited. Also, the play between gear teeth is cumulative with the number of gear meshings, causing objectionable gear chatter, vibration and deflection, all of which increase as the distance from the input power drive increases. In the case of photographic film processing machines, these defects are critical. They are the cause of damage to the delicate photographic film, the film emulsion can become marked, and the film can show the effect of the uneven transport through the system.